1. Field of the Invention
The present invention relates to a nanoball solution coating method and applications thereof, particularly to a nanoball solution coating method easy to operate and able to mass produce, and applications thereof.
2. Description of the Related Art
Kiyoshi Fujimoto, et al. proposed a paper “Organic Static Induction Transistors with Nano-Hole Arrays Fabricated by Colloidal Lithography” in 2005, and a paper “High-Performance, Vertical-Type Organic Transistors with Built-In Nanotriode Arrays” in 2007. In the two papers, a glass substrate is immersed in pure water and acetone, processed with an ultrasonic oscillator, dried, and then exposed to ultraviolet light/ozone for 20 minutes. Next, polystyrene nanoballs are electrostatically attached to the glass substrate, wherein the substrate is immersed in 0.01 wt % nanoball solution for 30 minutes to make nanoballs attach to the substrate saturatedly. Next, the substrate is immersed in ultrapure water heated to a temperature of 98° C. to flush away the residual nanoballs with the thermal current of hot water. Next, the substrate is flushed with cool water and dried. Thus is completed a process to attach nanoballs on a substrate. For the method, the uniformity of the nanoballs attached to the substrate is considerably influenced by the uniformity of the nanoball solution. Further, the process of the method is time-consuming and unfavorable for mass production.
Yu-Chiang Chao et al. proposed a paper “Polymer Space-Charge-Limited Transistor” in 2006, and a paper “Light-Emitting Polymer Space-Charge-Limited Transistor” in 2008. In the two papers, a substrate is immersed in a 0.4 wt % nanoball solution for tens of seconds; next, the substrate is immersed in heated isopropanol for 10 seconds to flush away the residual nanoballs with the thermal current of the heated isopropanol, whereby a single layer of nanoballs remains on the substrate. Then, the isopropanol on the substrate is rapidly dried with a nitrogen blower. The method is applicable to fabricate small-area elements but less likely to produce large-area elements. Besides, the products thereof lack stability.
Kun-Yang Wu et al. proposed a paper “High-Performance Space-Charge-Limited Transistor with Well-Ordered Nanoporous Aluminum Base Electrode” in 2011. Chi-Chih Ho proposed a paper “Fabrication of Monolayer of Polymer/Nanospheres Hybrid at a Water-Air Interface” in 2011. In the two papers, polystyrene nanoballs are suspended in water, and 1-3 ppm polystyrene oxide is added to the water to enhance coalescence of the nanoballs. Next, the nanoballs are deposited on a substrate. Next, oxygen plasma is used to shrink the nanoballs, whereby is obtained ordered nanopores. However, the process of the method is complicated and time-consuming and thus unfavorable to industrial application.
A Taiwan patent No. 097146142 disclosed a technology, which uses a spin-coating method to deposit nanoballs on a glass substrate, and uses oxygen plasma to control the size of the nanoballs. However, the spin-coating machine used by this method wastes a lot of nanoball material and impedes mass production.
A US patent of publication No. US2011/0048947 disclosed an electrostatic nanoball attaching method. In this method, the substrate is positively charged and immersed in a solution of negatively charged PS nanoballs for 2 minutes, wherein the solution is an aqueous solution having a sulfate and 1% PS nanoballs with a diameter of 100 nm. Next, the substrate is flushed with water for 1 minute. Next, the substrate is dried with a spin method or a nitrogen blower. The nanoballs are likely to be displaced or separated by surface tension of water during drying. Therefore, a low-surface tension solution is usually used to replace water. Besides, the method has too many steps and is unfavorable to mass production.
Accordingly, the present invention proposes a nanoball solution coating method and applications thereof to overcome the abovementioned problems.